 Burning plants to release the energy in them takes oxygen. Now when plants grow in water, the oxygen often bubbles out, rises, and goes up into the air, and so the plant is down there with less oxygen than it originally produced. And when the plant is burned, it may use up all the oxygen that's available unless currents pick up oxygen from the air and bring it down. Now what we're looking at here, the Mississippi River comes flowing down and it feeds the great Mississippi Delta, which is a huge pile of mud that's been carried down by the Mississippi. Out here is the Gulf of Mexico, clear water, and you can see the mud being washed off of the continent and carried into the ocean by the Mississippi, but mixed in with the mud, all the green you see here are plants, they're algae growing, and the algae give off their oxygen that goes to the air, and then when the algae die, they tend to sink a little bit and then they get burned and that may use up all the oxygen. And especially because fertilizer from human waste and from farms goes in the water and that fertilizes these blooms, they're often dead zones out here in the summer when there's no oxygen in the water. And that's the sort of situation that contributes to formation of fossil fuel, but it also kills fish and makes poison gas and all sorts of other things that we don't really like.